2. Welding difficulties and solutions
(1) Joints The head to be welded is ground with a sander to be inclined, and the arc is led at 10 mm at the top of the slope. After igniting the arc, move the arc to the bottom of the bevel. At this time, pay attention to the hole. If the melt hole is not formed, the back surface of the joint is not welded; if the melt hole is too small, the back of the joint is necked; if the hole is too large, the back weld is too wide or a weld is formed.
(2) When welding in flat position, it is easy to appear when the tumor is welded or not welded. If the gap is too large, it is easy to produce welding and welding operation. If the gap is too small, it is easy to produce one side or two sides. Unfused, the gap of the flat welding position should be controlled at about 2.5mm. When welding, the angle of the torch and the position of the wire pointing to the bath are extremely important. When the position is flat, the angle between the welding gun and the welding direction is 70°～80°, and the welding wire should be directed to the front 1/3 of the molten pool and make a slight lateral swing. If the molten pool is found to sink, the wire should be lifted while reducing the angle of the welding torch, and the dry elongation should be kept at 10 to 15 mm to prevent the welding.
(3) When standing welding, it is easy to appear unfused. During the vertical welding process, linear arcing should be used, and the angle between the welding gun and the welding direction is about 85° to 90°. If the speed of the downward welding is too fast, it is easy to produce one side or both sides are not fused; if it is too slow, there will be a phenomenon of iron accumulation or pre-conduction, which causes poor fusion on both sides of the groove and increases the labor intensity of the welder. decrease productivity. Therefore, the normal welding speed should be maintained during the vertical welding, and the thickness of the weld bead should be about 2.5mm.
(4) When welding in the up position, it is easy to appear the threading phenomenon and the concave position. When welding in the vertical position, the arc should be used for arc welding, and the angle between the welding gun and the welding direction is 80° to 90°. The wire should be directed at 1/3 of the front of the weld pool while maintaining a dry elongation of 10 to 15 mm. If the welding speed is too fast, the threading phenomenon will occur; the welding speed is too slow, and the iron liquid will fall easily, so that the angle of the front bead is too deep, and the back surface is concave, which causes defects such as slag inclusion or unmelting during welding.
(5) Arcing Before the end of welding, if the arc is improperly closed, craters are easily generated, and defects such as cracks and pores appear. Therefore, pay special attention to overcoming the customary action of hand arc welding when the arc is closed, that is, lift the welding rod upward. If the welding gun is lifted during RMD welding to receive the arc, the protection effect at the arc pit will be destroyed. At the same time, even if the arc pit is filled and the arc is extinguished, the torch can be removed after a few seconds at the crater to ensure reliable gas protection when the pool is solidified.
(6) Protective gas After using the gas cylinder for a period of time, pay attention to the cylinder pressure should be ≥1MPa, and the gas flow rate should reach 25L/min. Regularly check the air belt for air leakage. After each cylinder change, press and hold the air test button to discharge the air. Otherwise, air holes will be generated due to the doping of air.
(7) Wire feeding hose During the welding process, if the end of the welding wire is out of the ball and accompanied by a hopping phenomenon, the root will not be welded. This is because the wire feed hose is clogged, causing the wire feed speed to be too slow, and the welding current does not match, and the wire is burned back. Therefore, the wire feed hose should be cleaned regularly. Before purging the wire feeding hose, bend the wire feeding hose several times to loosen the internal blockage and then purify it with the air pump. Generally, it needs to be cleaned once every two welding wires are welded.
(8) Conductor nozzle If the welding wire is slightly shaken, or if there is a fire between the end of the wire and the contact tip, the contact tip should be replaced in time. Otherwise, it is easy to cause arc combustion instability, especially in the case of the upright welding, it is easy to cause the front angle to be too deep and the root to be unfused. In addition, the alignment of the welding wire, whether the air supply hole is blocked, and whether the shield is loose or not need to be checked in time.
(9) Ground wire and feedback wire Check whether the ground wire and the feedback wire are firmly connected, and keep the ground wire contact surface with metallic luster. If the ground wire is not securely connected, the current will be unstable. If the feedback line is not secure, it will not solder properly. When two welders are welding at the same time, if the welding parameters are unstable, the two welders and the connecting wires can be shielded.
(10) Welding posture Before welding, the welding posture should be determined in advance, and the welding position should be measured to avoid excessive joints caused by welding posture.
3. Conclusion
Since the application of the RMD welding process in the second-line pipeline project of the West-East Gas Pipeline, we have long studied the RMD welding process, summed up the difficulties of the above welding technology and its solutions, and conducted welding technical guidance for many construction units. , has been praised by the industry.
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